This invention concerns microbicidal compositions which include an isothiazolone and another biocide, and which are intended to provide more effective and broader control of micro-organisms in various industrial systems and for household products, agricultural products, and biomedical products, etc. In particular, the present invention relates to the use of a composition of 2-n-octyl-4,5-dichloro-isothiazolin-3-one, hereinafter referred to as 4,5-dichloro-2-octyl-3-isothiazolone, with tetrachloroisophthalonitrile.

The term "microbicidal" (or "antimicrobial" or "biocidal") as used herein is intended to encompass, but is not restricted to, all bactericidal, fungicidal and algicidal activity.

Isothiazolones are described in U.S.-A-3,761,488; 4,105,431; 4,252,694; 4,265,899 and 4,279,762, and elsewhere. Their use as microbicides is well known.

We have found that compositions formed from 4,5-dichloro-2-octyl-3-isothiazolone and tetrachloroisophthalonitrile afford unexpectedly good synergistic antimicrobial activity against a wide range of microorganisms: the disruptive action on the organisms by the two compounds together is unexpectedly greater than the sum of both compounds taken alone. This synergy does not arise from the expected activity of the components nor from the expected improvement in activity. As a result of the synergy, the effective dose required can be lowered, which is not only more economical but also increases safety margins. The synergistic compositions of the present invention provide more effective and broader control of microorganisms in a number of systems.

The present invention thus provides a composition having microbicidal activity which comprises 4,5-dichloro-2-octyl-3-isothiazolone and tetrachloroisophthalonitrile wherein the weight ratio of 4,5-dichloro-2-octyl-3-isothiazolone to tetrachloroisophthalonitrile is from about 150:1 to 1:250.

Important applications of the synergistic antimicrobial compositions of the present invention include but are not limited to: inhibiting the growth of bacteria and fungi in aqueous paints and coatings, adhesives, sealants, latex emulsions, and joint cements; preserving wood; preserving cutting fluids, controlling slime-producing bacteria and fungi in pulp and papermills and cooling towers; as a spray or dip treatment for textiles and leather to prevent mold growth; protecting paint films, especially exterior paints, from attack by fungi which occurs during weathering of the paint film; protecting processing equipment from slime deposits during manufacture of cane and beet sugar; preventing microorganism buildup and deposits in air washer or scrubber systems and in industrial fresh water supply systems; preserving fuel; controlling microorganisms contamination and deposits in oil field drilling fluids and muds, and in secondary petroleum recovery processes; preventing bacterial and fungal growth in paper coatings and coating processes; controlling bacterial and fungal growth and deposits during the manufacture of various specialty boards, e.g., cardboard and particle board; preventing sap stain discoloration on freshly cut wood of various kinds; controlling bacterial and fungal growth in clay and pigment slurries of various types; as a hard surface disinfectant to prevent growth of bacteria and fungi on walls, floors, etc.; as a preservative for cosmetic and toiletry raw materials, floor polishes, fabric softeners, household and industrial cleaners; in swimming pools to prevent algae growth; inhibiting the growth of harmful bacteria, yeasts, fungi on plants, trees, fruits, seeds, or soil; preserving agricultural formulations, electrodeposition systems, diagnostic and reagent products, medical devices; protecting animal dip compositions against the buildup of microorganisms, and in photoprocessing to prevent buildup of microorganisms, and the like.

The compositions of the invention may be added separately to any system or may be formulated as a simple mixture comprising the essential ingredients, and if desired a suitable carrier or solvent, or as an aqueous emulsion or dispersion.

The invention also provides a method of inhibiting or preventing the growth of bacteria, fungi or algae in a locus subject or susceptible to contamination thereby, comprising incorporating into or onto the locus in an amount effective to adversely affect the growth of said bacteria, fungi or algae any of the compositions defined above.

The compositions of the invention can be formulated as a solution in a wide range of organic solvents. The solutions generally contain about 5 to 30% by weight of the active composition. It is generally more convenient to provide the compositions in a water-diluted form: this may be accomplished by adding an emulsifier to the organic solution followed by dilution with water.

In general, the weight ratio of 4,5-dichloro-2-octyl-3-isothiazolone to tetrachloroisophthalonitrile may be in the range of from about 150:1 to about 1:250. The other specific and preferred ratios are given in the examples.

The synergism of two-component compositions is demonstrated by testing a wide range of concentrations and ratios of compounds, generated by two-fold serial dilutions in a Trypticase Soy Broth (Difco) growth medium of a microbicide in one dimension and another microbicide in the second dimension, against a bacterium Escherichia coli (ATCC 11229), or fungi Candida albicans (ATCC 11651), Aspergillus niger (ATCC 6275), or Aureobasidium pullulan (ATCC 9348). Each test tube was inoculated to make about 1-5 x 10⁷ bacteria per ml or 1-5 x 10⁵ fungi per ml. The lowest concentrations of each compound or mixtures to inhibit visible growth (turbidity) at 37° for E.coli and at 30°C for the fungi for 7 days were taken as the minimum inhibitory concentration (MIC). The MIC were taken as end points of activity. End points for the mixtures of compound A (4,5 dichloro-2-octyl-3- isothiazolone) and compound B (tetrachloroisophthalonitrile) were then compared with the end points for the isothiazolone A alone and compound B alone. Synergism was determined by a commonly used and accepted method described by Kull, F.C.; Eisman, P.C.; Sylwestrowicz, H.D. and Mayer, R.L., in applied Microbiology 9:538-541 (1961) using the ratio determined by$$\text{Qa/QA + Qb/QB = Synergy Index (SI)}$$ wherein

QA =

concentration of compound A in parts per million (ppm), acting alone, which produced an end point.

Qa =

concentration of compound A in ppm, in the mixture, which produced an end point.

QB =

concentration of compound B in ppm, acting alone, which produced an end point.

Qb =

concentration of compound B in ppm, in the mixture, which produced an end point

The test results for demonstration of synergism of microbicide combinations are shown in Table 1. This table concerns the combination of 4,5-dichloro-2-octyl-3-isothiazolone and tetrachloroisophthalonitrile, and shows:

• 1. test against E. coli, C. albicans (C. alb), A. niger or A. pullulan (A. pullul)
• 2. the end-point activity in ppm measured by MIC for compound A alone (QA), for compound B alone (QB), for compound A in the mixture (Qa), or for compound B in the mixture (Qb);
• 3. the calculation of synergy index (SI) based on the formula $\text{SI=Qa/QA + Qb/QB}$, and the weight ratio of 4,5-dichloro 2-n-octyl-3-isothiazolone (compound A) to tetrachloroisophthalonitrile (compound B) in the particular combination (A:B);
• 4. the range of weight ratios for synergism and the preferred weight ratios. It will be appreciated by those skilled in the art that the ratios given are approximate only.

The MIC values of each compound tested alone (QA or QB) are end-point activities except where the value is expressed as x.10. In these cases, the end-point activity was not seen at the highest tested concentration. For purpose of calculation of the synergy index and for operational definition of MIC, the reported value is twice the highest tested concentration. The value could be an underestimate of the true MIC; thus, the true synergy index could be even lower. Compound A = 4,5-dichloro-2-octyl-3-isothiazolone
Compound B = tetrachloroisophthalonitrile ORGANISM end-point activity in ppm calculations QA QB Qa Qb Qa/QA Qb/QB SI A:B C. alb 0.50 16.00 0.25 2.00 0.50 0.13 0.63 1:8 A. niger 16.10 32.10 0.25 16.00 0.02 0.50 0.51 1:64 16.10 32.10 8.00 0.50 0.50 0.02 0.51 16:1 A. pullul 16.10 16.00 2.00 8.00 0.12 0.50 0.62 1:4 16.10 16.00 8.00 1.00 0.50 0.06 0.56 8:1 C. alb 2.00 32.10 1.00 1.00 0.50 0.03 0.53 1:1 Synergistic ratios of compound A: compound B range from 16:1 to 1:64; preferred ratios are in the range of 8:1 to 1:8.

As can be seen by review of Table 1, the composition of the invention demonstrate synergistic microbicidal activity as measured by minimum inhibitory concentrations (MIC) and show surprisingly greater activity than the algebraic sum of the individual components which make up each composition.

In contrast, an example of nonsynergistic combination of 4,5-dichloro-2-octyl-3-isothiazolone and sodium dichlorophene is shown in Table 2. In this example of non-synergism, the microbial activities of either component as measured against E. coli and C. albicans are not affected by the presence or the absence of the other component in the combination. It is also not antagonistic because no loss of activity of either component in the combination was detected.

The synergistic activities of the compositions of the invention in most cases are applicable to bacteria, fungi, and a mixture of bacteria and fungi. Thus, the combinations not only lower the use-level of biocide but also broaden the spectrum of activity. This is especially useful in situations where either component alone does not achieve the best results due to weak activity against certain organisms. Compound A = 4,5-dichloro-2-octyl-3-isothiazolone
Compound B = Sodium dichlorophene ORGANISM end-point activity in ppm calculations QA QB Qa Qb Qa/QA Qb/QB SI A:B C. alb 4.10 16.00 No effect C. alb 16.00 32.00 No effect E. coli 16.00 62.00 No effect